Convoluted metal hose assemblies of the described type are used primarily in the aerospace industries, usually at temperatures well above 450.degree. F., although the official specifications require the hose to withstand violent and resonant vibrations at 850.degree. F. Primarily--but not exclusively--these hoses are often used to bleed off hot exhaust gases from areas of very high engine temperatures. These bled off gases might be used to monitor engine performance, for example. Therefore, a failure of the metal hose could spell a catastrophic failure of the entire aerospace vehicle. In addition, the bled off gas may also be used for de-icing a wing, preheating engine fuel, transferring exotic hyperbolic fuels, and the like.
For many reasons, these hoses are subjected to very high levels of vibrations, sometimes causing them to go into resonant vibrations. Therefore, the energy of such vibrations has to be absorbed, generally at the fitting interface, which is an area (usually very small) where a flexing body is transformed into a stiff and non-flexing body. Sometimes there is a sudden stiffness in the convoluted hose, which is caused by pressure surges of internal fluids. These and other events tend to concentrate material fatigue at fixed locations along the metal hose.
Heretofore, the interface area of hose-to-end fitting attachment has been one where stiff and flexible bodies are welded together so that bending occurs at a fairly sharp edge. The heat produced during the welding operation causes a heat affected zone in the convoluted metal hose which also appears at a point of maximum mechanical stress. These things combine to produce a weakness in the hose that leads to an early failure. Thus, the weld is a point of inherent weakness.
As a result of these considerations, a specification (AS 1424) for the metal hose joint design has been adopted by the commercial aircraft industry. This specification requires vibration testing at 850.degree. F., in combination with dynamic flexing and pressure surging, such as might be encountered in association with a jet engine. To date, it is thought that the assignee of this invention, the Titeflex Corporation, is the only company which has successfully met these specifications, for all sizes of hoses. When the assignee has encountered failures during their tests, they have occurred in the area of the weld or in the area that is heat affected by the welding process.